Site Collection moving throw error “site collection already exist Site collection will not be moved”

In preparation for the upgrade to Sharepoint 2013 I need to move all my sharepoint 2010 standard edition site collections “32” which they are in separate Databases content (SQL 2012) in one database content so I can run mount powers shell command to web application , I get the error :

Move-SPSite : Site collection http://sss database “name”. Site collection will not be moved
At line:1 char:12
+ Move-SPSite <<<< -Identity http://ssssss -DestinationDatabase name + CategoryInfo : InvalidData: (Microsoft.Share...PCmdletMoveSite:SPCmdletMoveSite) [Move-SPSite], SPCmdle tException + FullyQualifiedErrorId : Microsoft.SharePoint.PowerShell.SPCmdletMoveSite

Any help will be appreciated
Thanks